A combine with an axial separator is described in U.S. Pat. No. 3,828,794 A. The axial separator includes a rotor which has crop processing elements and which extends in the direction of travel of the combine and is arranged inside a housing. On the plate of the housing there are grates, through which threshed grains fall and are fed to a cleaning device. Spiral-shaped guide vanes are attached to the top side of the housing, which are used to lead the crop gradually backwards.
The guide vanes extend in spiral form radially relative to the axis of the rotor. The optimum pitch of the guide vanes, i.e., the degree by which their downstream end is shifted backwards against the direction of travel relative to the upstream end (or their angle to the rotor axis), can depend on the type of crop being processed. For crops with relatively small grains, such as wheat, it is important to maintain low power requirements for the axial separator, which means a relatively large pitch of the guide vanes, because the crop then leaves the axial separator faster, so that only a smaller amount of crop has to be moved in the axial separator. On the other hand, one goal for crops with rather large grains, such as peas and corn, is to keep the so-called dribble losses low. These losses are generated when the grains impact the guide vanes and are deflected in the direction towards the rear side of the axial separating device, where they leave the combine and are lost. To maintain low dribble losses, it is important that the guide vanes have a relatively small pitch. It is certainly possible to exchange the cover plates filled with guide vanes in order to adapt to the type of crop to be harvested, but this is very expensive.